Cranial sealing plug

ABSTRACT

Various embodiments of a burr hole plug assembly offer significant improvements for allowing lead and/or cannula access through a burr hole drilled through a patient&#39;s skull in connection with a Deep Brain Stimulation system, and subsequent sealing of such burr hole. The various burr hole plug assemblies described: (a) accommodate various burr hole sizes and provide a secure fit in the burr hole; (b) accommodate various locations for lead positioning and adjustment; (c) allow the lead to remain in a static position when the burr hole plug assembly is placed; (d) protect the lead from fracture at the exit location of the plug; (e) remain flush with the skull to avoid skin erosion and to eliminate unsightly flange protrusion from the patients&#39; skull; (f) adequately hold the lead in place over time; and (g) provide a selection of various types of burr hole plug assemblies and sizes for use by the implanting surgeon, thereby eliminating the need for surgeons to resort to custom plugs and plug assemblies made in the operating room specifically to fit a given patient.

The present application is a Divisional of U.S. application Ser. No.10/052,331, filed Jan. 18, 2002 which claims the benefit of U.S.Provisional Application Ser. No. 60/265,770, filed Jan. 31, 2001, whichapplications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to the field of implantable medicaldevices, including implantable electrodes. More particularly, theinvention relates to cranial sealing plugs used to seal a hole madethrough the skull of a patient for the purpose of inserting a medicaldevice and/or electrode into the brain. Even more particularly, theinvention relates to burr hole plugs which are flush with the surface ofthe skull. The embodiments described in the present invention may beused with a wide variety of burr hole sizes, which burr holes aretypically used to provide electrode or lead access to the brain inconnection with a Deep Brain Stimulation (DBS) system. It is to benoted, however, that the burr hole plug embodiments of the invention mayalso be used to seal holes made for the passage of other objects intothe brain, such as ablation catheters, drug delivery catheters, tissuedelivery catheters, and the like.

Deep Brain Stimulation is a medical procedure which involves access tothe brain through a burr hole placed in the skull for treatingParkinson's Disease, Essential Tremor, dystonia, chronic pain relief,and potentially the treatment of choice for other disorders. A typicalsurgical approach may include the following steps, of which only steps8, 31, and 32 relate directly to the present invention:

-   -   1. Attach the stereotactic frame on patient's head.    -   2. Obtaining an image of the various brain structures with MRI        or equivalent imaging modality of patient with stereotactic        frame.    -   3. Obtaining target identification using a planning software.    -   4. Positioning the patient with stereotactic frame in head rest.    -   5. Cutting the skin flap, exposing the working surface area of        cranium using scalp clips.    -   6. Placing the stereotactic arc with target coordinate settings        and identifying the location on the skull for creation of the        burr hole.    -   7. Removing the arc and drilling a burr hole.    -   8. Placing the base of the burr hole plug.    -   9. Placing the stereotactic arc with microelectrode recording        drive attached and appropriate stereotactic frame adaptor        inserted into instrument guide.    -   10. Inserting the recording microelectrode cannula and insertion        rod approximately 25 mm above the target.    -   11. Removing the recording microelectrode insertion rod, while        leaving recording microelectrode cannula in place.    -   12. Inserting the recording microelectrode such that the tip is        flush with the tip of the recording microelectrode cannula.    -   13. Attaching the connector pin of the recording microelectrode        to the microelectrode recording system.    -   14. Starting approximately 25 mm above target, begin the        microelectrode recording tract using the microdrive to advance        the microelectrode at a specified rate.    -   15. If the target is identified, prepare to place the        stimulating macroelectrode and proceed with step 16, if the        target is not identified proceed with the following:        -   a. Using recording results and pre-operative imaging,            determining a new set of coordinates for the theoretical            target.        -   b. Disconnecting recording microelectrode from the            microelectrode recording system.        -   c. Removing the recording microelectrode cannula and            recording microelectrode.        -   d. Continuing with the surgical process at step 10 above.    -   16. Removing the recording microelectrode cannula and recording        microelectrode.    -   17. Inserting a larger diameter insertion cannula and rod (the        tip of the slit insertion cannula and rod will be at a location        25 mm above target).    -   18. Removing the insertion rod, while leaving insertion cannula        in place.    -   19. Inserting a stimulating macroelectrode, and advancing to the        target stimulation site identified in step 15 above.    -   20. Using macrostimulation, simulating the stimulation of the        chronic

DBS lead to ensure proper results.

-   -   21. Removing the stimulating macroelectrode and cannula.    -   22. Inserting an insertion cannula and rod that accommodates the        DBS lead.    -   23. Removing the insertion rod.    -   24. Inserting the lead with stylet through the insertion        cannula.    -   25. Advancing the lead with the stylet to the target stimulation        site.    -   26. Once it is determined that the lead has been advanced to the        desired target location, connecting the connector of the lead to        a trial stimulator.    -   27. Performing the desired stimulation and measurements using        any one or combination of the four electrodes.    -   28. If results are favorable, then begin removal of the        insertion cannula and the stylet, and proceed with step 29, if        the results are not favorable then proceed with the following:        -   a. Using the macrostimulation results, microelectrode            recording results, and pre-operative imaging, determine a            new set of coordinates for the theoretical target.        -   b. Removing the lead and stylet.        -   c. Removing the insertion cannula.        -   d. Adjusting the coordinates of the stereotactic frame.        -   e. Continuing with the surgical process at step 10 above.    -   29. Removing the stylet followed by the insertion cannula.    -   30. Using macrostimulation verifying that microdislodgement of        the lead has not occurred.    -   31. Locking the lead in the burr hole plug.    -   32. Placing the burr hole plug cap.

Several inventions are known in the art that relate to burr hole plugsused for DBS application. As used herein, the term “burr hole plugs”relates to any device or assembly or system that includes one or morecomponents for insertion into a burr hole. Typically, a burr hole plugassembly includes at least two components: a ring or grommet-likeelement that is inserted into the hole first so as to protect the edgesof the burr hole (item 8 above), and a cap or plug device that isinserted into the ring or grommet-like element after the lead has beenpositioned in order to secure the lead and plug the hole.

By way of example, in U.S. Pat. No. 6,044,304, entitled Burr Ring withIntegral Lead/Catheter Fixation Device, a burr ring that is secured tothe skull portion of the brain is described. Patent '304 is incorporatedherein by reference. The burr hole plug described has an aperturecapable of accepting a lead through a septum. In addition the burr holeplug has an upper flange portion and circumferential ribs used toposition the plug in the cranium. The flange feature prevents the burrhole plug from being flush with the surface of the skull. Use of theribs in the manner suggested indicates that the material from which theplug and ribs are made is relatively rigid.

Another burr hole plug known in the art is described in U.S. Pat. No.6,006,124, which patent is incorporated herein by reference. The '124patent describes electrically connecting an implantable control moduleto a brain electrode. The '124 patent also describes a method of placingbrain electrodes beneath the scalp. No mention is made in the '124patent of a mechanical connection for the lead, nor of the mechanicalstability of the burr hole plug.

Still, with reference to U.S. Pat. No. 5,954,687, which patent isincorporated herein by reference, an apparatus is disclosed for securinga catheter within a burr hole. The apparatus described in the '687patent has a series of spaced septum elements that can be selectivelypenetrated for fluid communication with a reservoir in the apparatus.The main objective of the apparatus is to allow fluid access to thepatients' brain through a burr hole. Anchoring of the device is nottaught, and there are a limited predetermined number of septum holesthat can be accessed, thereby limiting use of the apparatus.

In yet another example, U.S. Pat. No. 5,927,277, which patent is alsoincorporated herein by reference, describes a burr hole ring forretaining a probe relative to the skull. The burr hole ring has anengaging member with holes to receive a probe. The '277 patent alsodescribes a method for securing a device at a desired orientation withinthe burr hole. Since a fixed spacing between holes is described, thislimits the number of locations that the device can be placed through theburr hole. The device described in the '277 patent consists of severalparts one of which contains a flange.

U.S. Pat. No. 5,865,842, incorporated herein by reference, teaches asystem and method for anchoring a lead in a burr hole. Such systemconsists of a base-plate, adaptor, seal, and screw cap. The lead isanchored mechanically at the burr hole at a 90 degree angle relative tothe burr hole. A flange protrudes from the burr hole of the skull.

In U.S. Pat. No. 5,843,150, incorporated herein by reference, an annularclamping means with a compressible feedthrough member for receiving alead is described. The described order for anchoring the lead includesmaking the burr hole, inserting the plug ring, inserting the lead, andengaging the clamping member. The embodiments described show an annularclamping means with protruding flanges.

Other burr hole plug assemblies, and features of burr hole plugs aretaught, e.g., in U.S. Pat. No. 5,464,446 (burr hole plug with a centrallumen and a cap that engages with the flange of the plug); U.S. Pat. No.4,998,938 (a device that facilitates insertion of an instrument into apatient's cranial cavity); U.S. Pat. No. 4,328,813 (a burr hole plugwith a cap that anchors the lead); and U.S. Pat. No. 4,245,645 (a probeand system that is used to perform stereoelectroencephalographicexploration). The burr hole plug applications described in theseadditional patents, including many lead insertion techniques, may alsobe used with the present invention. For that reason, the '466, 938, '813and '645 patents are incorporated herein by reference.

Despite the various types of burr hole plugs known in the art, asillustrated by the examples cited above, significant improvements arestill possible and desirable, particularly relative to a burr hole plugassembly that: (a) can accommodate various burr hole sizes and a securefit in the burr hole; (b) can accommodate various locations for leadpositioning and adjustment; (c) can allow the lead to remain in a staticposition when the burr hole plug is placed; (d) protect the lead fromfracture at the exit location of the plug; (e) is flush with the skullto avoid skin erosion and to eliminate any unsightly flange protrusionfrom the patients' skull (which can be especially important in thepopulation of older balding males); (f) adequately holds the lead inplace over time, eliminating the need for additional surgeries; and (g)provides a selection of various types of burr hole plugs that may beused by the medical industry, thereby eliminating the need forphysicians to resort to custom devices.

It is thus seen that there is a continual need for a variety of burrhole plug assemblies and lead securing methods for use therewith.

SUMMARY OF THE INVENTION

The present invention addresses the above and other needs by providing areliable method of sealing a burr hole using a sealing cranial plug thatcan accommodate various burr hole sizes and lead securing methods.

The invention disclosed and claimed herein provides various embodimentsof cranial sealing burr hole plug assemblies. Such assembliesaccommodate various burr hole sizes, provide various lead positioningfeatures, are adjustable and compressible, provide a design that isflush with the skull, and provide electrical connecting features fordetachably connecting a lead passing through the burr hole plug toexternal stimulating equipment.

In accordance with one aspect of the invention, there is provided acompressible burr hole plug assembly that can be inserted into a varietyof burr hole sizes and provides a radial force for positioning the lead.Advantageously, such embodiment is flush with the patient's skull andavoids unsightly flange protrusions which may cause skin erosion.

In accordance with another aspect of the invention, there is provided aburr hole plug assembly that accommodates various lead positions. Inaddition, the plug assembly provides a secure and flexible adjustmentfor the lead.

It is an additional feature of the invention to provide a burr hole plugassembly that accommodates excess lead length.

It is another feature of the invention to provide a burr hole plugassembly that includes a connecting feature for allowing a lead passingthrough the assembly to be detachably connected to other devices, suchas an implantable pulse generator. Such feature facilitates the use of apositioning stylet, a temporary cable for testing purposes in theoperating room, and other equipment used during the surgicalimplantation procedure. With such feature, electrical connection betweenan external stimulation device and the lead can be made at the burr holeplug connector, thereby forming a stimulation system. In such a system,the connecting device includes an extension with a connector that mateswith the lead at the burr hole plug assembly. The advantages forelectronically connecting the lead at the burr hole include: (1) therisk of lead fracture under the scalp is greatly minimized, if noteliminated; (2) the risk of lead failure at the burr hole exit point issimilarly minimized, if not eliminated; (3) the risk of the lead movingin the brain as a result of external disruption is virtually eliminated;and (4) if any part of the system fails external to the skull, brainsurgery is not required to replace the system.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will be more apparent from the following more particulardescription thereof, presented in conjunction with the followingdrawings wherein:

FIG. 1A is a top view showing a compressible burr hole plug ring made inaccordance with one embodiment of the invention;

FIG. 1B is a cross sectional view taken along line 1B-1B of FIG. 1A,showing the compressible burr hole plug ring;

FIG. 2A is a side cross sectional view of the compressible burr holeplug ring before it is placed in the burr hole of the cranium;

FIG. 2B is a side cross sectional view of a compressible burr hole plugring as it is placed in the burr hole of the cranium;

FIG. 3A is a top view of the compressible burr hole plug ring shown inFIG. 1A, and further including septum material positioned in the centerof the ring to thereby form a burr hole plug assembly, wherein theseptum material has a slit therein used for lead placement before theplug assembly is placed in the burr hole of the cranium;

FIG. 3B is a cross sectional view taken along line 3B-3B of FIG. 3A,showing the compressible burr hole plug assembly before it is placed ina burr hole of the cranium;

FIG. 3C is a top view of the burr hole plug assembly shown in FIG. 3Aafter it has been placed in a burr hole of the cranium;

FIG. 3D is a cross sectional view taken along line 3D-3D of FIG. 3C,showing the burr hole plug assembly inserted in the burr hole;

FIG. 4A is a top view of another embodiment of a burr hole plug assemblymade in accordance with the invention, which embodiment has a pivotpoint clamped configuration;

FIG. 4B is a top view of the assembly of FIG. 4A showing the clamp plugassembly in an open arrangement;

FIG. 5A is a top view of a burr hole and burr hole ring arrangementhaving multiple lead exit trajectories;

FIG. 5B is a top view of a clamp plug assembly accommodating onearrangement of lead exit trajectories;

FIG. 5C is a top view of a clamp plug assembly accommodating anotherarrangement of lead exit trajectories;

FIG. 6A is a top view of the burr hole plug assembly shown in an openconfiguration;

FIG. 6B is the side view of FIG. 6A, showing the open configuration ofthe burr hole plug assembly with a lead passing therethrough;

FIG. 6C is a top view of another embodiment of a burr hole plug assemblyproviding a clamped configuration;

FIG. 6D is the side view of FIG. 6C, showing the clamped configurationof the burr hole plug assembly with a lead passing therethrough;

FIGS. 7A, 7B, and 7C are similarly all top views of various burr holeplug rings having different outside diameters to accommodate burr holeplugs of different diameters, and further showing a clamp plug assemblyas an example of a type of plug that may be inserted in the rings;

FIGS. 8A, 8B, and 8C are side cross sectional views showing an offsetburr hole plug assembly cap which coils excess lead length in a cavityof the assembly as the burr hole cap is rotated;

FIGS. 9A, 9B, and 9C are side cross sectional views showing variouspositions of the same offset burr hole plug cap shown in FIGS. 8A, 8B,and 8C, and additionally illustrating the use of a “snap-cap” connectortherewith;

FIG. 10A is a top view of yet another embodiment of an offset burr holeplug assembly having a stabilizing access hole for capturing andsecuring the lead;

FIG. 10B is a cross sectional view taken along line 10B-10B of FIG. 10A;showing the offset burr hole plug assembly with a stabilizing accesshole;

FIG. 10C is a top view of the same offset burr hole plug assembly shownin FIG. 10A but with a lead placed in the stabilizing access hole;

FIG. 10D is a cross sectional view taken along line 10D-10D of FIG. 10C;showing the offset burr hole plug and lead;

FIG. 10E is a top view of the same burr hole plug shown in FIG. 10A withthe lead stabilized through a force exerted by insertion of a placementpin;

FIG. 10F is a cross sectional view taken along line 10E-10F of FIG. 10E;showing the offset burr hole plug assembly and stabilized lead;

FIG. 11A shows another embodiment of a burr hole plug assembly ring madein accordance with the invention;

FIG. 11B illustrates a “plug-in” connector used in conjunction with theburr hole plug assembly ring shown in FIG. 11A;

FIG. 11C is an exploded view of the burr hole plug assembly, showing thering of FIG. 11A and “plug-in” connector of FIG. 11B; and

FIG. 12 depicts a prior art embodiment of a burr hole ring with a flangeand ridges.

Corresponding reference characters indicate corresponding componentsthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principles of the invention. The scope of the invention shouldbe determined with reference to the claims.

Deep Brain Stimulation (DBS) is rapidly becoming an accepted procedureto treat diseases such as Parkinson's Disease, Essential Tremor,dystonia, the relief of chronic pain, and potentially the treatment ofchoice for other movement disorders. The present invention disclosesseveral burr hole plug assembly embodiments that can be used to seal aburr hole made into a patient's skull in order to allow lead access forstimulating the brain. The significant advantages of the several burrhole plug assembly embodiments presented herein will be described withreference to associated features shown in FIGS. 1A through 11C.

Referring first to FIGS. 1A and 1B, there is shown a compressible burrhole plug ring 10. The burr hole plug ring 10 is preferably made fromtwo biocompatible materials, a first rigid material 12 and a secondcompressible material 14. To maintain adequate rigidity the burr holeplug ring 10 comprises a combination of metal (or hard) member segments12 and elastic (or compressible) member segments 14. The material forthe rigid members 12 is made from epoxy, polyurethane, and titanium, oralloy compounds of epoxy, polyurethane, and titanium, or equivalentmaterials. The compressible elastic member 14 may comprise a suitableelastomer selected from the group consisting of: silicone rubber,polyurethane, or equivalent materials. A central hole 16 is used foraccepting a lead. The bottom edge 18 of the burr plug ring 10 ispreferably rounded or chamfered to facilitate entry of the plug ring 10into the burr hole 20, as shown in FIG. 2A.

As seen in FIG. 2A, the burr hole plug ring 10 has an outside diameterD1 larger than the diameter D2 of the burr hole. The burr ring plug 10is compressed by an insertion force F1 until its outside diameter D1equals D2. FIG. 2B shows the compressed burr plug ring 10′ inserted intothe burr hole 20. The compressible force F1 causes an equal and opposingforce F2 to be asserted against the edges of the burr hole of thecranium 22. This force F2 secures the burr hole plug 10′ in thepatient's skull. Advantageously, the reaction force F2 eliminates theneed for ridges on the outer diameter of the plug ring 10, and furthereliminates the need for a flange above the skull that acts to limit themotion in the X, Y, and Z directions 21, stabilizing the burr hole plugassembly in the burr hole.

A prior art embodiment of a burr hole assembly 13 with ridges 4, aflange 6 and septum material 8 in central hole 11 is shown in FIG. 12.As is evident from FIG. 12, the flange 6 would protrude above thepatients' skull when the ridge section 4′ is inserted in the burr hole.Disadvantageously, a protruding flange 6 may cause skin erosion, andcreates an unsightly bump in the head, especially in the patientpopulation of older balding males.

Referring next to FIG. 3A, there is shown an alternate embodiment of acompressible burr hole plug assembly 24 having a septum material 26contained within the central hole of the assembly 24 and a slit 28 forplacing a lead 30 and/or cannula. Placement of the plug assembly 24 canbe done before, during, or after placement of the lead. The septummaterial 26 may comprise silicone rubber or polyurethane or equivalentmaterials, and may have a porous or solid composition. When the burrhole plug assembly 24 is compressed in the burr hole, the septummaterial 26 is also compressed and thus applies a radial force aroundthe lead, thus acting to stabilize the lead 30. The burr hole plugassembly 24 with slit 28 thus enables placement around a lead 30 and/orcannula. The slit also allows for placement of the plug before, during,or after the lead is placed. The lead 30 is properly positioned by asurgeon using an apparatus such as a stereotactic frame. Thestereotactic frame is used to precisely localize an area in the brain bymeans of coordinates related to intra cerebral structures. U.S. Pat. No.4,350,159, discloses a stereotactic instrument used for preciseinsertion of an electrode in the brain. The '159 patent is incorporatedherein by reference. Once a lead or electrode has been inserted by thesurgeon in the localized position of the brain, it is important that thelead remain in place. A slight movement may cause injury to the brainand/or may cause the diagnosed area that is to be stimulated to bemissed. Therefore, use of a precise positioning instrument, such as astereotactic frame disclosed in the '159 patent, or an equivalentdevice, is preferred.

Referring back to FIG. 3A, a top view of the burr hole plug assembly 24is shown before insertion into the burr hole of the cranium 22 with aslit angle α1. FIG. 3B shows a cross sectional view taken along line3B-3B of FIG. 3A. As seen in FIG. 3B, the outside diameter D1 of theburr hole plug assembly 24 is larger than the diameter D2 of the burrhole 20. The burr hole plug assembly 24 is compressed by the force F1until its outside diameter D1 equals D2. FIG. 3C shows the compressedburr hole plug assembly 24′ inside the burr hole 20. At the compressedstage of the burr hole plug assembly 24, it can be seen that the angleα2 is less than the angle α1. The compressible force F1 causes anopposing radial force F2 to be generated, which opposing force securesthe burr hole plug assembly in the patients' cranium 22 as shown in FIG.3D. FIG. 3D is a cross sectional view taken along line 3D-3D of FIG. 3C.The compressed burr hole plug assembly 24′ and septum material 26 alsomaintains the lead 30 in the localized position established by thephysician.

Turning next to FIGS. 4A and 4B, there is shown a top view of analternate embodiment of a clamp plug assembly 32 having a pivot point 34and two half portions 32 a and 32 b. The embodiment shown in FIGS. 4Aand 4B has a clamp plug assembly 32 that accommodates multiple lead exittrajectories 38. The clamp arrangement of the burr hole plug assemblyhas the advantage that it can be placed around a lead and/or a cannularegardless of the exit point of the lead from the burr hole trajectory38 shown in FIG. 5A. FIG. 4B shows the open position of the clamp plugassembly 32. Each half portion 32 a and 32 b of the clamp plug assembly32 preferably has an edge material or coating 36, such as silicone, thatprovides an elastic component that minimizes crushing of the lead whenanchored in the clamp plug assembly 32.

FIG. 5A is a top view of a burr hole 39 showing five possible lead exittrajectories 38. The number of trajectories can vary depending on thesize of the burr hole 39 and target stimulation site. FIGS. 5B and 5Cshow the pivot point of the clamp plug assembly 32 in the burr hole 39in two arrangements accommodating various lead exit trajectories 38.

Next with reference to FIG. 6A and FIG. 6B, there is shown a top andside view respectfully of an alternate embodiment of a splitable burrhole plug assembly 40. The central slit 42 created by the two slidinghalf portions 40 a and 40 b of the splitable burr hole plug assemblyallows flexibility for positioning the lead. The same half portions 40 aand 40 b may also have a clamping burr hole plug arrangement 40′ asshown in FIG. 6C and FIG. 6D. Once the lead is positioned, the two halfportions 40 a and 40 b are closed. The lead 30 remains in its clampedposition due to the force F3 applied by the two half portions 40 a and40 b. It is obvious to one skilled in the art that different splitableburr hole configurations are possible.

Referring now to FIGS. 7A, 7B and 7C, there is shown a series of O-ringshaped inserts 52, 52′, and 52″ that can accommodate various size burrholes. Depending on the drill tool that a surgeon may prefer to useduring the drilling process of a burr hole in the patients' skull, eachburr hole may differ in size from patient to patient and surgeon tosurgeon. Therefore, the need for having a variety of inserts isadvantageous to the surgeon. The inserts shown in FIGS. 7A, 7B, and 7Ceach have different outside diameters ø2, ø3, and ø4, respectively, andsimilar inside diameters ø1 which can accommodate the same burr holeplug. The inside diameter ø1 of the inserts may be slightly smaller thanthe outside diameter D of the preferred plug. For example, FIGS. 7A, 7B,and 7C show the same pivot point clamp plug assembly 32, having twohalves 32 a and 32 b, and a diameter D, as shown in FIG. 4A, inserted inthe central hole of the O-ring type inserts 52, 52′, and 52″. Theinserts 52, 52′, and 52″ exert a force on the clamp plug assembly 32 tokeep the two halves in a closed position.

Turning next to FIG. 8A, there is shown a cross sectional view of analternate embodiment of a burr hole plug assembly 54 having a holecavity 56 and a plug cap 58. The plug cap 58 enables wrapping excesslead length 30′ in the hole cavity 56 of the burr hole plug assembly 54.The external end 31 of the lead 30 is attached to the cap 58. The cap 58is then rotated as shown by the arrow 60 in FIG. 8A, which rotatingcauses the lead length to be coiled within the hole cavity 56, as seenin the sequence of FIGS. 8A, 8B and 8C. The height of the excess leadlength and corresponding turns required to wrap the lead in the cavity56 of the burr hole plug 54 varies, depending on the type ofstereotactic frame used to position the lead. Other factors that mayvary, depending on the frame used are, the working lead length, thetarget distance (which is the distance measured from the surface of theskull to a reference point in the frame), the size of the burr hole, thelead diameter, and patient differences. As an example, for a burr holesize of 8 mm and a lead diameter of 1 mm, the Leksell StereotacticSystem manufactured by Elekta AB, located in Stockholm Sweden, wouldrequire a working lead length of 190 mm, a target site length of 85 mm,an excess lead length of 105 mm, and 4.2 turns to wrap the excess leadlength 30′ in the offset hole cavity 56. Another type of stereotacticframe available is the CRW Arc System manufactured by Radionics, locatedin Burlington Mass. As an example, for a burr hole size of 8 mm and alead diameter of 1 mm, the CRW Arc System requires a working lead lengthof 160 mm, a target site length of 85 mm, an excess lead length of 75mm, and 3.0 turns to wrap the excess lead length 30′ in the offset holecavity 56. Other examples of excess lead length and corresponding numberof turns in a burr hole plug cavity exist for various burr hole sizesand targets used in conjunction with the CRW and Leksell systems.

An alternate embodiment of an offset burr hole plug assembly 62 is shownin FIG. 9A. The same principle for positioning the lead 30 and rotatingthe excess lead length 30′ in the cavity 56 of the offset burr hole plug62 is similar as explained for FIGS. 8A, 8B, and 8C. Correspondingadjusting factors for the lead 30 with respect to the type ofstereotactic frame used are also similar as explained above. Theadditional feature found in the embodiment shown in FIG. 9A is anintegral “snap-cap” connector 64. The connector 64 can accommodate atemporary cable for testing purposes in the operating room or become apermanent connector to the implantable pulse generator, not shown. Theproximal end 31 of the lead shown in FIG. 9A can be preformed in a bentconfiguration 66 to reduce the stress on the lead 30 at the connectorlocation 68. Also shown in FIG. 9A, when the lead has a lumen therein, astylet 70 may be inserted into the lumen, and the preformed section ofthe lead would be straightened. Such stylet, if used, would be used onlyduring the initial insertion and placement of the lead through the burrhole. The stylet 70 is removed before the excess lead length is coiledwithin the cavity 56. FIGS. 9B and 9C are cross sectional views of theoffset burr hole plug assembly 62, showing the rotated excess leadlength 30′ in the plug assembly's cavity 56, and also showing theconnector closed by the pivot point 72.

Another alternate embodiment of an offset burr hole plug assembly 74 isshown in FIGS. 10A and 10B. FIG. 10A is a top view of the offset burrhole plug assembly 74 and FIG. 10B is a cross sectional view taken alongline 10B-10B of FIG. 10A. The offset burr hole plug assembly 74 is madeof an elastic biocompatible material and contains two openings, a pinhole 76 and a semi-circular slot hole 78. The semi-circular slot hole 78captures the lead 30 and the pin hole 76 accommodates a fixation rod 80.FIG. 10C shows the lead 30 in the semi-circular slot hole 78 and FIG.10D is a cross sectional view taken along line 10D-10D of FIG. 10C. Whenthe fixation rod 80 is inserted into pin hole 76, a force F4, shown inFIGS. 10E and 10F, is exerted against the lead 30, which in effectstabilizes the lead 30, and holds the lead in its desired position. Thefixation rod 80 may also act as an axis for rotating the excess leadlength around the cavity 82 of the offset burr hole plug 74, if neededor desired. FIG. 10F is a cross sectional view of FIG. 10E taken alongthe line 10E-10F of FIG. 10E.

The offset burr hole plug assembly 74 shown in FIGS. 10A through 10F canalso accommodate a “snap-cap” connector 64, shown in FIG. 9A, a“plug-in” connector 86, shown in FIG. 11B (discussed below), andvariable size inserts 52, 52′, and 52″ shown in FIGS. 7A, 7B, and 7C. Inthe case of using the “plug-in” connector 86, an offset burr hole plugring 84 has a radius groove 88, shown in FIG. 11A, to minimize thestress of the bend of the lead exiting the offset burr hole plug ring84.

Next, with reference to FIGS. 11A, 11B, and 11C, another embodiment of aburr hole plug ring 84 with an integral “snap-cap” connector 86 isshown. The burr hole plug ring 84 can accommodate a temporary connectorat surface 104 for testing in the operating room and a permanentconnector to the implantable pulse generator, not shown in the figures.In one embodiment, the temporary connector could also serve as the toolfor inserting the burr hole plug ring 84 into the burr hole of thecranium. The burr hole plug ring 84 is shown with a radius groove 88.The radius groove 88 minimizes the stress of the bend of the lead 30exiting the burr hole plug ring 84. Insertion holes 90A, 90B, 90C, and90D are located on the exposed surface 94 of the burr hole plug ring 84which accommodate corresponding connecting pins 92A, 92B, 92C, and 92D(not shown) located in the bottom surface 96 of the “snap-cap” connector86. As shown in FIG. 11A, ridges or threads 98 exist in the outersurface 100 of the burr hole plug ring 84. The ridges or threads 98screw into the burr hole to stabilize the burr hole plug ring 84 intothe burr hole. The opening 102 through the ring 84, goes through theentire thickness of the burr hole plug ring 84 and provides the entrancefor the lead into the diagnosed stimulating area of the brain. Inaddition, the burr hole plug ring 84 can also accommodate the inserts52, 52′, and 52″, shown in FIGS. 7A, 7B, and 7C, thereby allowing theplug ring 84 to be used with various sizes of burr holes.

As described above, it is thus seen that the present invention providesseveral burr hole plug embodiments (10, 24, 32, 40, 54, 62, 74, and 84),shown in FIGS. 1A through 11C. Each embodiment provides variousadvantages in providing a passage for a lead, ablation catheters, drugdelivery catheters, tissue delivery catheters, etc. Microelectroderecording equipment and macroelectrode stimulation equipment can also beplaced through the burr hole plug. Some embodiments contain a septummaterial or soft polymer that allows passage of all equipment and thatalso exert a radial force which in turn stabilizes the inserted lead orequipment. Other embodiments are made from a combination of rigid andcompressible material which when compressed provide a reaction forcewhich also stabilizes the inserted lead or equipment.

While the invention herein disclosed has been described by means ofspecific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope of the invention set forth in the claims.

What is claimed is:
 1. A method of using a cranial sealing plug assemblyincluding a first member and a second member adapted to fit togetherwith the first member to form an adjoining flexible interface, whereineach of the first and second members is a solid semi-circle, the methodcomprising: introducing an elongated medical device through a burr holeand into a brain of a patient; locating the elongated medical devicebetween the first and second members; selecting one of the exittrajectories for the elongated medical device; fitting the first andsecond members together to capture the elongated medical device withinthe adjoining flexible interface between the first and second members;and mounting the plug assembly into the burr hole, such that the plugassembly is flush with the patient's skull, and the elongated medicaldevice exits a burr hole aperture at the selected exit trajectory. 2.The method of claim 1, wherein the selected exit trajectory is locatedat a center of the burr hole aperture.
 3. The method of claim 1, whereineach of the first and second members comprises an outer circular edgethat coincides with the circumference of the burr hole when the plugassembly is mounted into the burr hole.
 4. The method of claim 1,wherein the first and second members are joined at a pivot point to forma pivoting clamp plug assembly configuration.
 5. The method of claim 1,wherein the first second members are configured to slidably engage witheach other to form a splittable clamp plug assembly configuration. 6.The method of claim 1, wherein the cranial sealing plug assembly furtherincluding at least one O-ring insert adapter having an outer diameter,the method comprising snugly fitting the O-ring insert adapter withinthe burr hole, and fitting the first and second members within theO-ring insert adapter.
 7. The method of claim 1, wherein one of the exittrajectories is located at a center of the burr hole aperture.
 8. Themethod of claim 1, wherein each of the first and second memberscomprises an elastic edge material adjacent the adjoining flexibleinterface with the first and second members fitted together.
 9. Themethod of claim 8, wherein the elastic edge material is composed ofsilicone.
 10. The method of claim 1, wherein each of the first andsecond members is a solid semi-circle.